It has been demanded that black pigments used in, for instance, paints and varnishes, ink, toner particles and-the coloration of rubber and plastic materials should be excellent in a variety of characteristic properties such as the degree of blackness, color hue, staining power and hiding power and that they must not be expensive. For this reason, there have conventionally been used, for instance, carbon black, iron oxide-containing paints represented by magnetite and other complex oxide pigments, depending on respective applications.
In all of the foregoing technical fields, there have recently been desired for the development of a technique for providing a pigment, which can not only satisfy the requirements of high-quality and high-performance, but also solve problems of, for instance, the environmental pollution and any adverse effect on the human body in case of, for instance, the foregoing carbon black and accordingly, the use thereof has been restrained. On the other hand, the iron oxide-containing pigments represented by magnetite do not suffer from the foregoing problems to such an extent-that carbon black suffers from the same, but the degree of blackness thereof is greatly dependent on the bonding conditions of Fe2+ ions present therein (or the quality of FeO). Moreover, these pigments suffer from such a problem that these Fe2+ ions (or FeO) are oxidized into Fe3+ ions. (or Fe2O3) or the pigments would undergo deterioration with the elapse of time.
As a technique relating to black pigments, which can eliminate the foregoing problems, the use of complex oxide-containing pigments comprising a variety of metal components have attracted special interest recently and there have been proposed complex oxide-containing black pigments each comprising, as principal metal components, at least two members selected from the group consisting of, for instance, copper, chromium, iron and manganese (see, for instance, Japanese Un-Examined Patent Publications Hei 9-124972 and Hei 9-237570).
However, the foregoing technique, which makes use of the complex oxide-containing pigments, is one using, as principal metal components, specific chemical substances specified as substances, which apply loads to the environment, such as copper, chromium and manganese (environmentally load-applying substances), as a result of the recent enactment of the municipal law concerning the Pollutant Release and Transfer Regiter.
Nevertheless, it is quite difficult to obtain an excellent black pigment, which can satisfy the requirement for the degree of blackness as one of the important characteristic properties of the black pigment while reducing the content of the foregoing environmentally load-applying substances to a level as low as possible and there has not yet presently been developed any satisfactory black pigment.
Accordingly, it is an object of the present invention to provide black complex oxide particles suitably and mainly used as a black pigment for paints and varnishes, ink, toner particles, and rubber and plastic materials, having a low load applied to the environment and an excellent degree of blackness as well as a method for the preparation of such black complex oxide particles.